OBJECTIVE: The purpose of this study was to determine whether maternal prepregnancy overweight/obesity has independent effects on breastfeeding initiation and duration and whether these effects are different for women who experience medical problems during pregnancy or labor/delivery complications in comparison with those who have no medical or labor/delivery complications. METHODS: We used the early childhood longitudinal study-birth cohort data. Kaplan-Meier survival functions, logistic, and Cox regression modeling were used in the analyses. RESULTS: Findings indicate that overweight/obese women with medical or labor/delivery complications were less likely to initiate breastfeeding in comparison with their counterparts of normal weight. We did not find an independent effect of prepregnancy overweight/obesity on breastfeeding initiation among women with no medical problems. This group of women, however, had an 11% increased risk of stopping breastfeeding with each additional month of breastfeeding duration in comparison to those of normal weight. CONCLUSIONS: It is important to evaluate the health history and pregnancy complications among overweight/obese mothers in developing interventions for successful initiation and duration of breastfeeding.